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CRS-7 Launch Update

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Re: CRS-7 Launch Update

#41

Post by drzaiusapelord »

nkoren wrote: post #34
drzaiusapelord wrote: post #32

Earlier quoted context omitted.

Stupid question perhaps, but don't we have the ability to 100% simulate the rocket physics and the code it runs on in a simulation environment? Or are they just punching out code, shoving it onto rocket controllers, and testing in the real world? I'm curious as to the QA system used here. I imagine with proper simulation this should have been catchable. I wonder if SpaceX's low cost approach means cutting certain cor…

Rocket physics are actually relatively trivial and, yes, can be fully simulated (and are). Rocket plumbing is always the hard part. Perhaps the threads on some connector got stripped as it was screwed together. Perhaps there was a manufacturing flaw or unexpected bit of corrosion in a particularly vital bolt. Perhaps a bit of contamination in a fuel line caused something catalytic to happen. Perhaps a bit of excess H…

I guess my point is, can we do a full simulation of every screw, material, plumbing, liquid dynamics, weather dynamics, etc and augment those with known fail scenarios and other fuzzy data to build out a real world KSP that predicts fails reliably? We should understand how things like corrosion and condensation work on a rocket engine. Considering the low cost of incredible amounts of CPU power, granular level simulation is possible on a certain level today if someone wanted to create it. We certainly see this kind of thing with stealth technology, where we can simulate every permutation of near every radar photon hitting the various surfaces of planes with various materials, scenarios, temperatures, etc.

I imagine this level of simulation might not be entirely feasible yet. Maybe for the lack of trying or budget. In a growth industry or one powered by both commercial and technical pressures, it may be difficult to sit down and build something like this out. From a more practical point of view, it may make sense to just let things explode than spend years running expensive simulations instead of building things, launching, and collecting paychecks.

Re: CRS-7 Launch Update

#42

Post by rwhitman »

nkoren wrote: post #33
rwhitman wrote: post #30

Earlier quoted context omitted.

After watching the press conference yesterday I got the sense that Musk's tweets aren't particularly helpful for SpaceX press relations

The thing is -- despite all the "Iron Man" winks and glamour of being a billionaire who wants to colonise Mars, etc. -- Elon is truly, deep down, a nerd's nerd. Which means that his respect for the PR department is probably roughly proportional to how much duct tape they've wrapped around his head.

The PR effort in this case was being lead by Gwynne Shotwell who is the President & COO. He was apparently tweeting information that his COO wasn't prepared to comment on yet. That doesn't send a good message about leadership confidence to people in his organization regardless of how much of a "nerd's nerd" he's trying to present himself as

Re: CRS-7 Launch Update

#43

Post by onewaystreet »

rwhitman wrote: post #30
beltex wrote: post #12

"Cause still unknown after several thousand engineering-hours of review. Now parsing data with a hex editor to recover final milliseconds." 4:09 AM - 29 Jun 2015 https://twitter.com/elonmusk/status/615431934345216001

After watching the press conference yesterday I got the sense that Musk's tweets aren't particularly helpful for SpaceX press relations

SpaceX was criticized after its early failures for not being transparent enough, so Musk is probably still reacting to that.

Re: CRS-7 Launch Update

#44

Post by ygra »

anotherangrydev wrote: post #40
timsally wrote: post #38

Earlier quoted context omitted.

Can you be more specific? If you have a partial piece of data (say because the data was streaming and a rocket exploded), the parser for that data is unlikely to work out of the box. Hence the use of a hex editor.

Yeah, but why not write your own temporary parser or whatever. They (should) have top-class software engineers in there, why they don't just make a quick and dirty script to sort out whatever they're looking for? IDK, that tweet felt like when you're watching a movie and then the 'hacker' comes around and you see a lot of props on the screen that are designed to excite 'geeks'. Like, right now, a lot of guys should b…

Some hex editors allow you to actually define an ad-hoc data format to parse, e.g. http://www.x-ways.net/winhex/templates.html – it doesn't have to be ed(1) for hex data. Besides, it could just have been a choice of words meant to convey that they have a bunch of incomplete/corrupted data that needs manual interpretation.

Re: CRS-7 Launch Update

#45

Post by drzaiusapelord »

makmanalp wrote: post #37
drzaiusapelord wrote: post #32

Earlier quoted context omitted.

Stupid question perhaps, but don't we have the ability to 100% simulate the rocket physics and the code it runs on in a simulation environment? Or are they just punching out code, shoving it onto rocket controllers, and testing in the real world? I'm curious as to the QA system used here. I imagine with proper simulation this should have been catchable. I wonder if SpaceX's low cost approach means cutting certain cor…

I don't think we have the ability to 100% simulate anything - I don't doubt for a second that a lot of this stuff is being simulated already, and I think you may be severely overestimating just how useful any doable simulation is in terms of catching a bug like this one. You have literally hundreds of systems working in concert and tied to more hundreds of physical components coming under extreme temperature and pres…

>You have literally hundreds of systems working in concert and tied to more hundreds of physical components coming under extreme temperature and pressure conditions

This is exactly what computers are for: doing hard stuff we can't do on paper or just by real world prototype testing. I imagine this is a hard problem, but it may be so because from a time/budget perspective it may just make financial sense to let stuff blow up now and again, than build out such a system.

I kinda see this as the difference between writing typical code versus writing code that's deterministic. The former is cheaper/faster but the latter is safer but more expensive and slower. In growth industries or when you have a strict schedule on your back, the slower approach is often ignored.

>Quoth Feynman

Feynman died when the hottest CPU was the 386. We simply have the capabilities, at least in hardware, for non-trivial simulation that during Feynman's time would have required CPU resources ridiculous to even speculate about. Safe assumption in Feynman's world (1918-1988), at least in regards to technology and engineering, may not be safe assumptions in our world. The same way our assumptions today won't make too much sense for our grandchildren. They might be bewildered by the idea that rocket fails were constant and common, the same way I'm bewildered by things like hot-days causing vapor lock to shut down old cars or, say, occasionally tuning a carburetor. We have electric gas pumps and computer controlled fuel injectors now.

edit: to reply to jacquesm. That's a pretty bold claim about O-rings. We fully understand the materials they're made of, their typical decays, etc. They're not magic. If someone wanted to make a top-down simulation that included, well, everything, it certainly seems possible to me, and while certainly not perfect, if done right, should provide positive outcomes. The real question is, what's the incentive? Spend billions and years doing this for one system (which may be old or even obsolete by the time the simulation is complete) or just accept the occasional preventable loss. Seems the latter approach just makes more sense financially, but that doesn't mean the former approach must be impossible. Many things are possible that just aren't incentivized.

Re: CRS-7 Launch Update

#46

Post by imglorp »

dlgeek wrote: post #7
dabeeeenster wrote: post #2

"Preliminary analysis suggests the vehicle experienced an overpressure event in the upper stage liquid oxygen tank approximately 139 seconds into flight. Telemetry indicates first stage flight was nominal and that Dragon remained healthy for some period of time following separation." Sounds like they are trying to suggest that if there had been people in the capsule they would have survived...

The manned capsule has a powered abort system, and this one doesn't, so they really don't need to suggest anything (since a failure here would not be reflective of the surviviability of Dragon2). They intentionally disable ("safe") the parachute system during the launch phase, but from the rumors I'm hearing coming out of SpaceX, if they had been enabled, this capsule would have survived.

Maybe all the cargo shots should have these systems enabled to further exercise them. It would have been nice to demonstrate capsule survival in yesterday's event.

Re: CRS-7 Launch Update

#47

Post by mikeash »

anotherangrydev wrote: post #40
timsally wrote: post #38

Earlier quoted context omitted.

Can you be more specific? If you have a partial piece of data (say because the data was streaming and a rocket exploded), the parser for that data is unlikely to work out of the box. Hence the use of a hex editor.

Yeah, but why not write your own temporary parser or whatever. They (should) have top-class software engineers in there, why they don't just make a quick and dirty script to sort out whatever they're looking for? IDK, that tweet felt like when you're watching a movie and then the 'hacker' comes around and you see a lot of props on the screen that are designed to excite 'geeks'. Like, right now, a lot of guys should b…

How are you going to figure out how to write that quick and dirty script without looking at the raw data in a hex editor to figure out how it's been corrupted?

Far from BS, pointing a hex editor at your data dump sounds like the very first thing you'd do when you get some data that your software can't immediately read.

Re: CRS-7 Launch Update

#48

Post by mikeash »

imglorp wrote: post #46
dlgeek wrote: post #7

Earlier quoted context omitted.

The manned capsule has a powered abort system, and this one doesn't, so they really don't need to suggest anything (since a failure here would not be reflective of the surviviability of Dragon2). They intentionally disable ("safe") the parachute system during the launch phase, but from the rumors I'm hearing coming out of SpaceX, if they had been enabled, this capsule would have survived.

Maybe all the cargo shots should have these systems enabled to further exercise them. It would have been nice to demonstrate capsule survival in yesterday's event.

It's not something you merely "enable." These cargo missions are using Dragon 1 capsules, whereas the manned system is Dragon 2. The abort system in Dragon 2 is integral to the capsule (it doubles as the landing system used after a normal flight) and isn't something you can just retrofit to a different vehicle.

Re: CRS-7 Launch Update

#49

Post by Serow225 »

JshWright wrote: post #29
phkahler wrote: post #21

My thoughts on this. Overpressure in the LOX tank could be due to 1) failure to vent properly or 2) something heating it up. Option 1 is based on the fact that it's constantly evaporating and needs to vent. This seems really unlikely given that it passed all test on the pad 2 minutes before. It also sounds like this was likely ruled out based on Elon's tweet about a "counter intuitive cause". Option 2 sounds like fir…

There are plenty of other scenarios... The IDA is the heaviest thing they have ever carried in the trunk, AFAIK. Maybe its mounting bracket failed and it impacted the top of the second stage, buckling the LOX tank. A suddenly induced crack allowed some LOX to escape (the initial 'puff'), and the suddenly reduced pressure allowed the rest of the LOX to boil off and the tank to BLEVE, causing the catastrophic failure o…

Interpreting Musk's tweet about 'counter-intuitive' meaning BLEVE would make sense to me.

Re: CRS-7 Launch Update

#50

Post by juandopazo »

drzaiusapelord wrote: post #32
colomon wrote: post #16

Earlier quoted context omitted.

Ugh, now imagining trying to debug a really sneaky bug that costs $100 million every time it triggers...

Stupid question perhaps, but don't we have the ability to 100% simulate the rocket physics and the code it runs on in a simulation environment? Or are they just punching out code, shoving it onto rocket controllers, and testing in the real world? I'm curious as to the QA system used here. I imagine with proper simulation this should have been catchable. I wonder if SpaceX's low cost approach means cutting certain cor…

The book The Martian, big-budget movie coming soon, has some pretty awesome fictional-yet-very-well-informed situations of things that were so unimaginable to have an impact on anything and still caused things to go terribly wrong. Highly recommended.
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